1. Field of Invention
The present invention relates to novel rheological modifiers and more particularly it relates to aqueous fluid polymer suspensions of hydrophobically modified polyacrylates, polyurethanes and poly(acetal- or ketal-polyethers).
2. Description of the Prior Art
It is desired by the latex paint industry to employ liquid rheology modifiers, rather than powders, for ease of incorporating these into paint formulations. A number of liquid thickeners are commercially available either in the form of solutions of these polymers in mixed solvents, or in the form of aqueous suspensions of these polymers as is described in the prior art references cited below.
In contrast to the prior art thickeners for paint containing volatile organic solvents it is preferred by the paint industry, as an environmental safeguard, to incorporate ingredients into latex paint that have little or no volatile organic compounds (VOCs) present. Thus, it is preferentially desired to employ water as a carrier medium with which to add these polymers to the paint.
It has been found in the prior art that water can be modified with various salts such as diammonium phosphate, diammonium sulfate or sodium formate salt to convert this medium to a non-solvent carrier for suspensions of specific water-soluble polymers. For example, U.S. Pat. No. 4,883,536 describes suspensions of hydroxyethylcellulose prepared in concentrated aqueous solutions of diammonium sulfate or diammonium phosphate, and that these suspensions in turn were useful for rheology modification of latex paint. U.S. Pat. No. 5,228,908 describes that concentrated aqueous sodium formate solution can be employed for preparation of fluid suspensions of the polymers such as hydroxyethylcellulose as well. In U.S. Pat. No. 5,578,168 the use of a number of salts, including sodium formate, were shown to be useful for preparing aqueous suspensions of poly(ethylene oxide). In U.S. Pat. Nos. 5,541,241 and 5,489,638 it was demonstrated that sodium formate and other salts were useful for preparing aqueous suspensions of polyvinyl alcohol.
None of the above polymers described in the prior art aqueous fluidized polymer suspensions, however, exhibit all of the desired features of latex paint thickeners. Specifically fluidized polymer suspensions of hydroxyethylcellulose or hydrophobically modified hydroxyethylcellulose, as described in U.S. Pat. No. 4,883,536 or 5,228,909, typically provide poor flow and leveling to the latex paint, along with an undesirably low high shear (ICI) viscosity. It was therefore desired to create a liquid thickener that would have improved performance in latex paint compared to these prior art thickeners. It was also desirable to combine, if possible, different latex paint rheological modifiers in one liquid carrier so that a combination of properties could be imparted to the latex paint.
According to the present invention there is provided an aqueous fluid polymer suspension comprising a water-soluble synthetic associative thickener, a water soluble carbon containing salt selected from the group consisting of sodium and potassium salts of aliphatic and aromatic carboxylic acids and sodium and potassium carbonate, and water. The polymer can be selected from the group consisting of hydrophobically modified polyurethanes, hydrophobically modified polyacrylates and hydrophobically modified poly(acetal- or ketal-polyethers) comprising a backbone of poly(acetal- or ketal-polyether) which has ends that are capped with hydrophobic groups independently selected from the group consisting of alkyl, aryl, arylalkyl, alkenyl, arylalkenyl, cycloaliphatic, perfluoroalkyl, carbosilyl, polycyclyl, and complex dendritic groups wherein the alkyl, alkenyl, perfluoroalkyl, and carbosilyl hydrophobic groups comprise 1 to 40 carbons, and the aryl, arylalkyl, arylalkenyl, cycloaliphatic and polycyclyl hydrophobic groups comprise 3 to 40 carbons.
In another aspect, the present invention provides a process for preparing an aqueous fluid polymer suspension of a water-soluble synthetic associative thickener polymer comprising dissolving the carbon containing salt in water and adding the polymer to and mixing it with the salt solution.
According to the present invention there are further provided processes for thickening aqueous systems by adding the aqueous suspension of the hydrophobically modified water-soluble polymers of the present invention thereto.